1. Field of the Invention
The present invention relates to a noise existence diagnosis device for a fuel injection system.
2. Description of Related Art
JP-A-2008-144749 (US 2008/0228374), JP-A-2009-74535 (US 2009/0056678), or JP-A-2010-223185 (US 2010/0250095) describes a fuel pressure sensor which detects a pressure of fuel downstream of a common rail (pressure accumulating container). A change of the fuel pressure generated with fuel injection is detected as a fuel pressure waveform. A change in injection rate of fuel is analyzed based on the detected waveform as an injection state.
For example, a point of inflexion in a start of lowering in the fuel pressure which appears in the waveform is detected, and injection start time can be calculated based on the time when the point of inflexion appears. Moreover, a lowering speed (inclination) of the fuel pressure which appears in the waveform is detected, and a raising speed in the injection rate (inclination) can be calculated based on the lowering speed.
If an actual injection state is known by the analysis, feedback control can be performed for operation of a fuel injection valve based on the injection state, so that the fuel injection state can be controlled with high accuracy.
However, electric noise may overlap with the fuel pressure waveform detected with the sensor because many electric actuators, such as an electric throttle valve and an EGR valve, exist near the sensor. When a signal wire of the sensor is located near a power supply line of the electric actuator, the noise overlap is generated with high possibility. When noise overlaps on the fuel pressure waveform in this way, analysis accuracy of the injection state gets worse and it becomes impossible to control the fuel injection state with the high accuracy.
High frequency noise may be removed from the fuel pressure waveform using a low pass filter circuit. However, complete removal of the noise is difficult, although such filter circuit can reduce an amplitude of the high frequency noise, based on characteristics of the circuit.
The noise overlap cannot be known only using the low pass filter circuit.